Pipe pontoon floating roof

ABSTRACT

A floating roof for large storage tanks incorporating large diameter pipes to provide additional buoyancy and stiffening for the roof. An annular box pontoon provides a portion of the required roof buoyancy. Large diameter chordal pipes are used to stiffen the flat circular deck located inside the annular pontoon while providing additional distributed buoyancy and structural stability to said deck.

[ 1 Sept. 12, 1972 FOREIGN PATENTS 0R APPLICATIONS 688,536 6/1964 Canada..... ....220/26 R 1,116,442 5/1956 France................ ....220/26 R 1,290,265 3/1962 France......... ......220/26 R 641,063 6/1962 Italy................,..; ....220/26 R Pn'mary Examiner-M. Henson Wood, Jr. Assistant Examiner-Edwin D. Grant Attorney-F. Donald Paris et al.

[57] ABSTRACT A floating roof for large storage tanks incorporating large diameter pipes to provide additional buoyancy and stiffening for the roof. An annular box pontoon provides a portion of the required roof buoyancy. Large diameter chordal pipes are used to stiffen the flat circular deck located inside the annular pontoon while providing additional distributed buoyancy and structural stability to said deck.

6 Claims, 3 Drawing Figures ....B65d 87/18 ........220/26 R, 26 D ....220/26 D .....220/26 R .220/26 D United States Patent Guber, Jr.

[54] PIPE PONTOON FLOATING ROOF [72] Inventor:

22 Filed:

[21 Appl.No.: 155,809

[51] Int.

[58] Field Search...

mmmwm m m N M r. u mmmmom m iih n HLWWJM 462658 445566 999999 111111 WWWWfiU I 1 64 7782 1 0 646 934022 501586 222233 P'ATENTEDSEP 12 1912 INVENTOR Few Q1/5551? BY 1 ATTORNEY TEFL PIPE PONTOON FLOATING ROOF BACKGROUND OF THE INVENTION Large storage tanks used for hydrocarbon materials in refineries are provided with roofs to prevent water from entering the tanks and to cut down on evaporation losses. They are normally of two types, one being a so-called cone roof tank having a peaked roof atop the tank which remains in a fixed position without regard to the level of the hydrocarbon within the tank. The other type is the floating roof tank which has a roof floating on top of the hydrocarbon that moves up and down as the volume of hydrocarbon enclosed within the tank changes. The first or cone roof type tank has a disadvantage in that the tank breathes, that is, as the tank is filled hydrocarbon containing vapors are expelled from the tank vent and, conversely, when the tank is emptied air from the outside is drawn into the tank through the vent. Moist air may condense inside the tank causing water build-up therein and more importantly, the air brought in may form explosive mixtures in the tanks vapor space. As hydrocarbon vapors are expelled when the tank is filled, a loss of material is sustained which also contributes to the pollution of the surrounding air, unless a vapor recovery system is provided. Commonly, for volatile hydrocarbons the second type or floating roof tank is used. With this type of tank the disadvantages of the cone roof tank are eliminated, but the design of a floating roof is complex and introduces various problems which are not associated with the conical roof. Particularly troublesome problems are how to remove accumulations of rain water on the roof which could otherwise cause it to sink, how to obtain a proper seal between the periphery of the roof and the tank wall and how to maintain the structural integrity of the roof in the larger sized tanks.

Any floating roof must have buoyancy'if it is to float on top of the hydrocarbon and not sink in the tank. Three basic roof constructions commonly used have been disclosed in US. Pat. No. 2,954,223 which lists these as pan-type, double deck and annular pontoon.

The pan-type roof is the simplest possible, being made like a pan being open at the top and having raised sides. No fully-enclosed space is used to provide buoyancy. With this type of roof any leakage or accumulation of fluid on top of the roof would destroy or reduce its buoyancy and the roof would be in danger of sinking.

The double deck roof contains two levels of steel decking which enclose an air space thus providing in-' herent buoyancy. It is more expensive to construct and introduces the possibility of accumulation of explosive mixtures between the set of deck plates.

The annular pontoon roof is a combination of the two previous roofs, wherein an enclosed box member is provided at the circumference of the tank along the wall. The enclosed box provides buoyancy and minimizes the possibility of the roof sinking should some fluid accumulate on the roof deck. A single roof deck is used, filling the center of the ring formed by the annular box pontoon.

The single center deck used with the annular pontoon is satisfactory for smaller tanks but for larger tanks the single deck becomes quite flexible and problems develop not found in smaller tanks. It has been found that excessive sag of the roof decking occurs thus providing low points for accumulation of rainwater and making it difficult to drain the water properly. In addition, the single deck is prone to cracking caused by the stresses which may be placed on it as the roof flexes. It has been found that wind-induced rippling may cause mechanical failure of the roof. Buckling of the pontoons has also occurred as a result of radial forces generated by' accumulations of rain or snow. In order to overcome the problems inherent in the annular pontoon single deck floating roof, the roof of the present invention has been developed. A more rigid construction is achieved which is less subject to failure in service. Such failure, of course, would necessitate the emptying of the tank and removing it from service for repair, which would not only be expensive but would cause operating difficulties for the refinery which uses the tank. The roof of the present invention will permit the use of floating roofs in the larger size tanks expected to be used in the near future, taking advantage of the inherent safety, convenience and reduced cost of the larger size tankage. Used in new or existing tankage, it will minimize problems of structural stability, drainage, and wind-induced deflections.

SUMMARY OF THE INVENTION The invention disclosed herein is an improved annular pontoon single deck floating roof. The roof comprises an annular box-pontoon member located along the inner circumference of a storage tank, typically for hydrocarbons. On the annular pontoon, between the pontoon and the inner wall of the tank, is mounted one of the known types of sealing devices to provide a moveable seal between the roof and the wall. Spanning the inside of the annular pontoon member are sections of single deck roof plates supported primarily by the buoyancy of large diameter commercially available pipe which forms an integral part of the roof. The pipe is disposed as an array of chordal members across the annular pontoon ring. A central chord through the center and perpendicular to the other chordal pipes consists of a large diameter pipe member or, alternatively, a box member similar to that used for the annular pontoon. Drains are provided within this diametral pontoon in order to drain rainwater or any other accumulated fluid off the roof and out of the tank through the usual internally articulated drain leg. Vents are provided to release any hydrocarbon vapor or air which may be trapped between the pipe pontoons under the deck and, in addition, limit the rain water which might accumulate on the deck between the pontoon members if the articulated drain leg is out of service. A complete description of the floating roof of the present invention will be set forth below in correspondence to the drawings illustrating the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a tank for hydrocarbon or other use embodying the pontoon floating roof of the present invention shown in a partially cut-away perspective view.

FIG. 2 is an enlarged section taken substantially along line 2-2 of FIG. 1 illustrating the pipe pontoons of the present invention.

FIG. 3 is an enlarged view taken substantially along line 33 of FIG. 1 illustrating the box pontoons and drain of the specific embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 presents a perspective view of a tank for storage of hydrocarbon or other liquids embodying the floating roof of the present invention which incorporates the use of pipe for pontoons for strengthening and adding buoyancy to the floating roof. The outer shell of the tank may be 100 feet or more in diameter. A floating roof is often used in such tanks in order to minimize evaporation and prevent rainwater from entering the stored fluid. The floating roof, as its name implies, moves up and down within the tank to accommodate changes in volume of liquid stored and floats on top of said liquid. The pontoon in the view shown in FIG. 1 comprises a roof structure with a circumferential pontoon 12 extending completely around the tank. The space between the outer edge of pontoon l2 and the tank wall is filled by seal shown here simply as a flexible member which will adjust for changes in relative position'of the tank wall and the outer pontoon 12. Other and more complex steel mechanisms have been described in U.S. Pats. Nos. 2,802,591 and 3,120,902. More complex fabric seal assemblies are also available. Additional buoyancy is provided by the center box pontoon 14 but the primary purposes of this member are to provide a central structural member to facilitate construction, to act as a collector for rain water and to serve as the base for installation of a rollingladder. The parallel array of chordal pipe pontoons 16 which extends across the floating roof and intersects the center box pontoon 14 provides distributed buoyancy and structural reinforcement for the deck plate 18 which extends completely between the pipe pontoons 16, the center box pontoon 14 and the circumferential pontoon 12. The combination of the foregoing elements completes a structurally sound roof which is sufflciently buoyant to float on the liquid contained in the tank, moving up and down with changes in the liquid level. Buoyancy of the roof is determined by optimum selection of diameter, thickness, and spacing of the chordal pipe pontoons so that the deck plate is at the surface of the liquid. Sufficient structural integrity is provided in large tanks by the chordal pipe pontoons 16 thus assuring that wind-induced rippling will not cause break-up of the roof section damaging it or, in the extreme case, sinking the roof.

Inasmuch as the floating roof is below the top of the tank 10, it will collect rain water. In time sufficient water would accumulate to sink the roof into the hydrocarbon which is of a lower density than the rain water. To prevent this from occurring and in order to remove the water as it collects, drain holes 22 are provided in the sides of the center box drain 14. These openings 22 connect to the interior of a drain whereby the rain water will'flow from the roof deck plate 18 through the opening 22 and thence to drain connection 26. Water, after entering connection 26, then passes through an articulated pipe or flexible hose 28 as illustrated in FIG. 1. The hose or pipe 28 can accommodate the movement of the roof relative to the tank wall. The

flexible drain hose 28 passes the collected rain water through nozzle 30 to an outside drain. Nozzle 30 may be provided with a valve which is designed to shut off automatically should a leak occur and hydrocarbon begin to pass through the drain connection to the outside, thereby avoiding emptying the tank and the hazards attendant thereto.

Inasmuch as air or vapors may collect in small quantities under the floating roof, it is desirable to remove these insofar as is possible. Removal of said vapors retains the deck plate 18 in contact with the contents of the tank and therefore minimizes the effective surface from which evaporation can take place. For this purpose a vent 24 is provided in each of the deck plate sections between the pipe pontoons 16 where air or vapors could be trapped. The vent 24 is sized to be high enough so that rain water which would collect on the deck plate 18 could not build up and spill over into the hydrocarbon in the tank during normal operation. These vents also act as emergency drains and eliminate the possibility of sinking the roof due to accumulated rain water if the normal drain system 28 is inoperative. Use of these vents as emergency drains is possible because of the distributed buoyancy provided by the chordal pipe pontoons.

FIG. 2 illustrates an enlarged section of the floating roof taken substantially along line 22 of FIG. l. A portion of the center box drain 14 is shown with the opening 22 therein for collecting rain water and in a cut-away view the drain connection 26. The vent from the deck plate 24 also is visible in this view. In addition, accessory opening 17 is shown on top of each of the pipe pontoons 16. It will be seen that with this structure that rain water can collect between the pipe pontoons 16 making it necessary for such water to be drained through openings 22. Also, air or vapors could be trapped between the pipe pontoons which would require venting through vent 24.

FIG. 3 shows another enlarged cross sectional view along line 3--3 of FIG. 1 which illustrates an outer edge of the circumferential pontoon 12 and after a broken section the center box pontoon 14. In this view the flexible seal 20 between the circumferential pontoon l2 and the tank wall 10 is schematically illustrated. Also, the deck plate 18 and the center box pontoon with drain opening 22 and drain connection 26 can be seen.

The preferred embodiment disclosed herein may be varied without departing from the scope of the invention as defined by the claims which follow.

What is claimed is: g

l. A floating roof for a storage tank comprising:

a. a circumferential pontoon having seal means disposed between said pontoon and the wall of said storage tank;

b. a drain pontoon disposed across the diameter of said circumferential pontoon, whereby water is collected from said roof;

0. chordal pontoons disposed perpendicularly to said drain pontoon and extending across said circumferential pontoon;

d. deck plate means attached to said circumferential drain and chordal pontoons and extending between said pontoons and covering open areas bounded thereby.

6 2. The floating roof of claim 1 wherein said chordal a. a circumferential pontoon having a seal disposed pontoons are fabricate from pipe. between said pontoon and the wall of said storage 3. The floating roof of claim 1 wherein said drain tank;

pontoon is fabricated from pipe.

4. The floating roof of claim 1 wherein the said drain 5 pontoon has openings positioned to receive water collecting on the deck plates and a bottom drain for removal of said collected water.

5. The floating roof of claim 1 wherein said deck feremial pontoon; plate has vent means whereby gases collecting under 10 d. deck plate attached to said pontoons and extendsaid deck plate may be released while preventing water from flowing inside said storage tank mg between said pontoons and covering open 6. In combination, a storage tank and a floating roof areas bounded thereby therefor, said floating roof comprising:

b. a drain pontoon disposed across the diameter of said circumferential pontoon, whereby water is collected from said roof;

c. chordal pontoons disposed perpendicularly to said drain pontoon and extending across said circum- 

1. A floating roof for a storage tank comprising: a. a circumferential pontoon having seal means disposed between said pontoon and the wall of said storage tank; b. a drain pontoon disposed across the diameter of said circumferential pontoon, whereby water is collected from said roof; c. chordal pontoons disposed perpendicularly to said drain pontoon and extending across said circumferential pontoon; d. deck plate means attached to said circumferential drain and chordal pontoons and extending between said pontoons and covering open areas bounded thereby.
 2. The floating roof of claim 1 wherein said chordal pontoons are fabricated from pipe.
 3. The floating roof of claim 1 wherein said drain pontoon is fabricated from pipe.
 4. The floating roof of claim 1 wherein the said drain pontoon has openings positioned to receive water collecting on the deck plates and a bottom drain for removal of said collected water.
 5. The floating roof of claim 1 wherein said deck plate has vent means whereby gases collecting under said deck plate may be released while preventing water from flowing inside said storage tank.
 6. In combination, a storage tank and a floating roof therefor, said floating roof comprising: a. a circumferential pontoon having a seal disposed between said pontoon and the wall of said storage tank; b. a drain pontoon disposed across the diameter of said circumferential pontoon, whereby water is collected from said roof; c. chordal pontoons disposed perpendicularly to said drain pontoon and extending across said circumferential pontoon; d. deck plate attached to said pontoons and extending between said pontoons and covering open areas bounded thereby. 